Story highlights

Washington (CNN)Donald Trump again warned of another 9/11-like attack on the United States if refugees are continually allowed into the country.

"Our country has enough difficulty right now without letting the Syrians pour in," the presumptive Republican nominee said in an interview on the National Border Patrol Council podcast Sunday morning, as first reported by BuzzFeed.

On The Green Line podcast Trump also suggested ISIS is paying for refugees' cell phone plans.

"They all have cell phones so they don't have money, they don't have anything, they have cell phones," Trump said. "Who pays their monthly charges, right? They have cell phones with the flags, the ISIS flags on them."

Trump has repeatedly brought up the cell phones of Syrian refugees throughout his primary campaign, though its unclear what evidence he's referencing regarding their content.

Read More

When asked if he thought it would take an attack similar to 9/11 for the country to "wake up about border security," Trump agreed.

"Bad things will happen; a lot of bad things will happen," Trump said. "There will be attacks that you wouldn't believe. There will be attacks by the people that are right now coming in to our country."

Since the start of the refugee crisis, 2,166 Syrians have been settled in the U.S., following a two-year vetting process.

Trump also spoke about Hillary Clinton's agenda for immigration reform and his own plans for border control, including his proposal to build a wall at the Southern border. The National Border Control agents' union made its first-ever endorsement of a presidential candidate when it backed Trump in March.